1. Field of the Invention
This invention relates in general to directional antenna systems using electronically controllable sweep of the beam.
2. Description of the Prior Art
Directional antenna systems with controllable beam direction, for example, in radar technology for purposes of target tracking and in satellite communication transmission systems for alignment of an on-board antenna of a space missile so as to align it to a remote station on the ground as well as for communication transmission via tropo-scatter arrangements are known. In principle, there is the possibility of producing a sweep of the beam of the directional antenna with mechanical means which sweeps the antenna or by mechanically displacement of the primary radiator with respect to the reflector. However, as a practical matter, such mechanical solutions are not feasible when relatively high speed of shifting from one beam direction to another are required. In tropo-scatter applications, for example, in which brief fading of signals occur, it is necessary to change the direction of the beam within one to three .mu. seconds so as to maintain error free operation. As described in the publication Merrill Skolnik, Radar Handbook, McGraw-Hill Book Company, New York, 1970, Chapter 11, Pages 6 and 7 there are a number of possibilities of producing a sweep of the beam direction utilizing electronic techniques by means of a radiator arrangement consisting of a plurality of radiators. In the final analysis, all of these various possibilities operate by influencing the direction by means of a feed of the radiator elements of the radiator field which varies in phase with the phase front of the resultant electromagnetic wave and this results in a change of the beam direction.
The publication Leon J. Ricardi entitled Multibeam Antennas Communication Satellite Antenna Technology Seminar, Boston University, Oct. 31 through Nov. 4, 1977, discusses electronically steering the beam direction of a directional antenna by means of changing the position of the primary radiator arrangement by utilizing different primary radiators of the primary radiator arrangement which are activated as a function of the desired beam direction. Difficulties exist with regard to the realization of the wiring and switching system for the various primary radiators in this technique. This is particularly true in the case where two or more primary radiators must respectively cooperate for the desired beam formation to sweep the antenna beam in its direction.